In an automotive industry, frictional characteristics of many engine parts are crucial for cost reduction due to maintenance, parts replacement and breakage, reduction of investment cost by extending a life-span, and energy saving by reducing friction in addition to energy saving. In particular, the surface morphology in contact with each other wear has a significant impact on friction behaviors in the friction characteristics. In the case of sliding contact in a lubricated state, the frictional characteristics can be improved by the formation of surface irregularities such as a small dimple shape. These irregularities serve as a lubricant reservoir and serves to prevent a lubricant from leaking out. In addition, since abrasive particles can be removed from a contact surface and collected inside a structure, additional abrasion can be prevented, which is caused due to the abrasive particles.
Therefore, in recent years, studies have been conducted by various methods to enhance fuel efficiency and energy loss due to friction in power machine parts by reducing the energy loss due to friction resistance of engine parts and among these methods, in particular, a research into surface texturing has in active progress.
Surface texturing technology represents machining a large number of irregularities such as dimples or grooves on at least one surface of two surfaces in order to improve lubrication between two surfaces that are relatively moving through the lubricant. The irregularities of the surface store the lubricant and promote generation of hydrodynamic pressure by abrasion particle trapping.
In particular, laser surface texturing is mainly used to make patterns in the form of the dimples and as compared with other texturing methods, a process time is extremely fast and the shape and size of the dimples can be controlled by using laser parameters (pulse energy, pulse number) and in the case of research trends of the laser surface texturing, S, Schreck et al. in Germany has researched that performs texturing of channel and dimple types with respect to Al2O3 and 100Cr6 steels by using an Nd:YAG laser and reduce the friction according to their density under lubrication and Izhak Etsion of Israel has experimentally confirmed that a partial pattern is further improved than total patterning using the laser surface texturing in a cylinder ring, which is in direct contact with a cylinder in an internal combustion engine. In addition, Kovalchenko of the Argonne Institute in the United States has suggested that when there is the dimple based on a friction coefficient and the wear scar of the ball according to the dimple density using laser surface texturing (hereinafter, referred to as LST) and the viscosity of the lubricant, the wear rate of the ball was high, but a contact area increases as compared with an initial contact and the transition from boundary lubrication to a mixed lubrication region thus rapidly occurs in a lubricated state, thereby decreasing the friction coefficient.
However, even in the above-mentioned research, it is necessary to develop a new type of low-friction member which improves a low friction effect due to an insufficient low friction effect through the laser surface texturing technology.